FOUR TYPES OF RANDOM ACCESS MEMORY
Types of RAM
There are different types of RAM that are used in computer systems, each having its own features and uses.
Memory types include:
Description:-
30-pin SIMM (Single In-line Memory Module) Computer Memory Module sticks using the 30-Pin SIMM format are listed on this page. A 30 pin memory card has 30 pins [or fingers] on each side of the memory module board; how ever, the pins on either side of the PWB are connected together. The memory module may appear to have 60 pins when in fact there are only 30 unique signal pins. 30 pin SIMMs used only an 8-bit data bus perhaps 9-bits using ECC. In this case ECC may also be called Parity.
At last check 30-pin SIMMs had an access time of 60nS, which is very slow by today's standards. The Pin Out and Signal names for a 30-Pin SIMM module is listed below.
30 pin SIMM modules are obsolete, replaced by 72-pin SIMMS, and no longer used.
30 pin SIMM modules are obsolete, replaced by 72-pin SIMMS, and no longer used.
In fact 72-pin SIMMs are obsolete, as SIMM modules were later replaced by DIMM memory modules.
Pinouts of memory modules using the 72 pin format may be found on the PC Memory Modules page.
Refer to the Computer Memory Modules page for additional pinouts and memory module descriptions, memory module types, memory terms and current memory standards.
Pinouts of memory modules using the 72 pin format may be found on the PC Memory Modules page.
Refer to the Computer Memory Modules page for additional pinouts and memory module descriptions, memory module types, memory terms and current memory standards.
| Pin # | Signal name | Signal Description |
|---|---|---|
| 1 | VCC | +5 VDC |
| 2 | /CAS | Column Address Strobe |
| 3 | DQ0 | Data 0 |
| 4 | A0 | Address 0 |
| 5 | A1 | Address 1 |
| 6 | DQ1 | Data 1 |
| 7 | A2 | Address 2 |
| 8 | A3 | Address 3 |
| 9 | GND | Ground |
| 10 | DQ2 | Data 2 |
| 11 | A4 | Address 4 |
| 12 | A5 | Address 5 |
| 13 | DQ3 | Data 3 |
| 14 | A6 | Address 6 |
| 15 | A7 | Address 7 |
| 16 | DQ4 | Data 4 |
| 17 | A8 | Address 8 |
| 18 | A9 | Address 9 |
| 19 | A10 | Address 10 |
| 20 | DQ5 | Data 5 |
| 21 | /WE | Write Enable |
| 22 | GND | Ground |
| 23 | DQ6 | Data 6 |
| 24 | A11 | Address 11 |
| 25 | DQ7 | Data 7 |
| 26 | QP | Data Parity Out |
| 27 | /RAS | Row Address Strobe |
| 28 | /CASP | Something Parity |
| 29 | DP | Data Parity In |
| 30 | VCC | +5 VDC |
02. 72-pin SIMM
72 pin SIMM modules are obsolete and no longer used. SIMM modules were replaced by DIMM memory modules.
The pinout for 72 pin SIMM memory is listed in the table below.
72-pin memory modules have been obsolete for some time now. 72-pin memory modules should not be used in new designs.
Refer to the main Computer Memory Modules page for an updated listing of current memory module formats.
DDR/DDR2 formats are in mass production, refer to Memory Module manufacturers page for detailed coverage.
The pinout for 72 pin SIMM memory is listed in the table below.
72-pin memory modules have been obsolete for some time now. 72-pin memory modules should not be used in new designs.
Refer to the main Computer Memory Modules page for an updated listing of current memory module formats.
DDR/DDR2 formats are in mass production, refer to Memory Module manufacturers page for detailed coverage.
The 72-pin SIMM pin out table describes an outdated memory module which is no longer in production.
SIMM memory is obsolete and should be replaced by DIMM modules in new systems.
The signal names or signal assignments and pin numbers are still valid, but relate to an out-dated memory stick
SIMM memory is obsolete and should be replaced by DIMM modules in new systems.
The signal names or signal assignments and pin numbers are still valid, but relate to an out-dated memory stick
| Pin | Non-Parity | Parity | Description |
|---|---|---|---|
| 1 | VSS | VSS | Ground |
| 2 | DQ0 | DQ0 | Data 0 |
| 3 | DQ16 | DQ16 | Data 16 |
| 4 | DQ1 | DQ1 | Data 1 |
| 5 | DQ17 | DQ17 | Data 17 |
| 6 | DQ2 | DQ2 | Data 2 |
| 7 | DQ18 | DQ18 | Data 18 |
| 8 | DQ3 | DQ3 | Data 3 |
| 9 | DQ19 | DQ19 | Data 19 |
| 10 | VCC | VCC | +5 VDC |
| 11 | n/c | n/c | Not connected |
| 12 | A0 | A0 | Address 0 |
| 13 | A1 | A1 | Address 1 |
| 14 | A2 | A2 | Address 2 |
| 15 | A3 | A3 | Address 3 |
| 16 | A4 | A4 | Address 4 |
| 17 | A5 | A5 | Address 5 |
| 18 | A6 | A6 | Address 6 |
| 19 | A10 | A10 | Address 10 |
| 20 | DQ4 | DQ4 | Data 4 |
| 21 | DQ20 | DQ20 | Data 20 |
| 22 | DQ5 | DQ5 | Data 5 |
| 23 | DQ21 | DQ21 | Data 21 |
| 24 | DQ6 | DQ6 | Data 6 |
| 25 | DQ22 | DQ22 | Data 22 |
| 26 | DQ7 | DQ7 | Data 7 |
| 27 | DQ23 | DQ23 | Data 23 |
| 28 | A7 | A7 | Address 7 |
| 29 | A11 | A11 | Address 11 |
| 30 | VCC | VCC | +5 VDC |
| 31 | A8 | A8 | Address 8 |
| 32 | A9 | A9 | Address 9 |
| 33 | /RAS3 | /RAS3 | Row Address Strobe 3 |
| 34 | /RAS2 | /RAS2 | Row Address Strobe 2 |
| 35 | n/c | PQ3 | Parity bit 3 (for the 3rd byte, bits 16-23) |
| 36 | n/c | PQ1 | Parity bit 1 (for the 1st byte, bits 0-7) |
| 37 | n/c | PQ2 | Parity bit 2 (for the 2nd byte, bits 8-15) |
| 38 | n/c | PQ4 | Parity bit 4 (for the 4th byte, bits 24-31) |
| 39 | VSS | VSS | Ground |
| 40 | /CAS0 | /CAS0 | Column Address Strobe 0 |
| 41 | /CAS2 | /CAS2 | Column Address Strobe 2 |
| 42 | /CAS3 | /CAS3 | Column Address Strobe 3 |
| 43 | /CAS1 | /CAS1 | Column Address Strobe 1 |
| 44 | /RAS0 | /RAS0 | Row Address Strobe 0 |
| 45 | /RAS1 | /RAS1 | Row Address Strobe 1 |
| 46 | n/c | n/c | Not connected |
| 47 | /WE | /WE | Read/Write |
| 48 | n/c | n/c | Not connected |
| 49 | DQ8 | DQ8 | Data 8 |
| 50 | DQ24 | DQ24 | Data 24 |
| 51 | DQ9 | DQ9 | Data 9 |
| 52 | DQ25 | DQ25 | Data 25 |
| 53 | DQ10 | DQ10 | Data 10 |
| 54 | DQ26 | DQ26 | Data 26 |
| 55 | DQ11 | DQ11 | Data 11 |
| 56 | DQ27 | DQ27 | Data 27 |
| 57 | DQ12 | DQ12 | Data 12 |
| 58 | DQ28 | DQ28 | Data 28 |
| 59 | VCC | VCC | +5 VDC |
| 60 | DQ29 | DQ29 | Data 29 |
| 61 | DQ13 | DQ13 | Data 13 |
| 62 | DQ30 | DQ30 | Data 30 |
| 63 | DQ14 | DQ14 | Data 14 |
| 64 | DQ31 | DQ31 | Data 31 |
| 65 | DQ15 | DQ15 | Data 15 |
| 66 | n/c | n/c | Not connected |
| 67 | PD1 | PD1 | Presence Detect 1 |
| 68 | PD2 | PD2 | Presence Detect 2 |
| 69 | PD3 | PD3 | Presence Detect 3 |
| 70 | PD4 | PD4 | Presence Detect 4 |
| 71 | n/c | n/c | Not connected |
| 72 | VSS | VSS | Ground |
| PD1 | PD2 | PD3 | PD4 | Size | Access time |
|---|---|---|---|---|---|
| GND | GND | - | - | 4 or 64 MB | - |
| NC | GND | - | - | 2 or 32 MB | - |
| GND | NC | - | - | 1 or 16 MB | - |
| NC | NC | - | - | 8 MB | - |
| - | - | GND | GND | - | 50nS, 100nS |
| - | - | NC | GND | - | 80nS |
| - | - | GND | NC | - | 70nS |
| - | - | NC | NC | - | 60nS |
The edge connector pin-outs for the 72 PIN SIMM [Single Inline Memory Module] is listed in the table above.
The follow up tables provide the size and access times.
Notes: A9 is a N/C on 256k and 512k modules.
A10 is a N/C on 256k, 512k, 1M and 4M modules.
RAS1/RAS3 are N/C on 256k, 1M and 4M modules.
Data width is 32 bits per memory stick [the front 72 pins and back 72 fingers on the card are connected together]
The follow up tables provide the size and access times.
Notes: A9 is a N/C on 256k and 512k modules.
A10 is a N/C on 256k, 512k, 1M and 4M modules.
RAS1/RAS3 are N/C on 256k, 1M and 4M modules.
Data width is 32 bits per memory stick [the front 72 pins and back 72 fingers on the card are connected together]
The approximate board size. 4.25" x 1.0"
SIMM: Single Inline Memory Module. SIMM's have pins on the front and back of the card, but they are connected together.
DRAM: Dynamic Random Access Memory
FPM:Fast Page Mode: (asynchronous) Obsolete, faster than normal DRAM, used in 386/486 computers.
EDO: Extended Data Out: (asynchronous) A superset of FPM, just faster than FPM.
All 72 pin SIMMs use either EDO or FPM memory. 72 pin SIMM modules are obsolete and no longer used.
72 pin SIMMs have an alignment notch on the bottom left to side, and a notch in the center of the PWB.
DRAM: Dynamic Random Access Memory
FPM:Fast Page Mode: (asynchronous) Obsolete, faster than normal DRAM, used in 386/486 computers.
EDO: Extended Data Out: (asynchronous) A superset of FPM, just faster than FPM.
All 72 pin SIMMs use either EDO or FPM memory. 72 pin SIMM modules are obsolete and no longer used.
72 pin SIMMs have an alignment notch on the bottom left to side, and a notch in the center of the PWB.
03. 168-pin DIMM (Dual In-line Memory Module)
04. 184-pin DIMM
184 Pin DIMM. 184 Pin DIMM. DDR SDRAM is the newest of the memory types under development that will be available in the 184 Pin DIMM form factor. The principle difference between conventional SDRAM and DDR SDRAM is its ability to read/write data on both edges of a clock, therefore resulting in faster data transfer.
The text descriptions refer to the different physical packaging of memory chips. This packaging is the placement of individual memory chips on a printed circuit board (PCB) which is designed to be easily inserted or connected to the motherboard.
Within each of the types there are different speeds, capacities and architecture. This means that even although a memory module could fit into a memory slot on the motherboard it may not work and that reference should be made to the motherboard documentation when installing new memory.
SDRAM
This stands for Synchronous Dynamic Random Access Memory and is a special type of DRAM that can be found in most new machines. The memory module will normally be a 168-pin DIMM. SDRAM is faster than asynchronous memory because the memory is synchronised with the system bus and clock, and therefore, the processor
Common descriptions of SDRAM include PC66, PC100 and PC133, with the numeric part indicating the memory speed in Mhz.
Common storage sizes of SDRAM memory modules range from 16MB to 2GB and over.
Static RAM
Static Random Access Memory (SRAM) retains its contents by having a constant source of power applied. This differs from Dynamic Random Access Memory (DRAM) that needs to be regularly refreshed for the memory cells to maintain their state.
SRAM is faster and consumes less power than DRAM, however, because of this it is slightly more expensive.
Due to the nature of its data storage SRAM takes up more space for less memory than DRAM does. This is known as its density. DRAM can store more and is therefore more suited to low cost, high capacity systems, such as a PCs main memory.
The application of SRAM is more likely to be on the processor itself or in the form of a small but very fast cache memory.
WHAT IS DIMM?
A DIMM (dual in-line memory module) is a double SIMM (single in-line memory module). Like a SIMM, a DIMM is a module that contains one or several random access memory (RAM) chips on a small circuit board with pins that connect it to the computer motherboard.
A SIMM typically has a 32 data bit (36 bits counting parity bits) path to the computer that requires a 72-pin connector. For synchronous dynamic RAM (SDRAM) chips, which have a 64 data bit connection to the computer, SIMMs must be installed in in-line pairs, since each one supports a 32-bit path. A single DIMM can be used instead. Originally, a DIMM had a 168-pin connector to support 64-bit data transfer.
As faster dynamic random access memory (DRAM) was developed, DIMM circuit boards evolved. Modern DIMMs based on double data rate fourth generation (DDR4) SDRAM chips use 288-pin connectors to attach to the computer motherboard to enable the increase in data throughput. As clock speeds of the RAM chips increased, the 64-bit path handled increasing amounts of data.
Another evolution in DIMMs is the use of cooling fins or structures attached directly to the DIMM. The increase in chip density in typical 8 gigabyte (GB) or 16 GB DIMMS, and the increase in clock speed, led to an increase in heat production. This was made worse by the fact that DIMMs based on DDR4 RAM chips can be produced in capacities up to 64 GB.
Cooling structures on the DIMM help vent that heat into the computer enclosure and away from the motherboard and CPU.
SO-DIMM
While the standard DIMM is in the form of a rectangular stick approximately 5.5 inches in length, the small outline dual in-line memory module (SO-DIMM) is about half that size at 2.74 inches long. Both types of DIMMs are most commonly 1.2 inches tall, but both are made in a very low profile (VLP) format that is only 0.8 inches tall.
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