IBM PC/XT DRAM memory calculation

In summary, the IBM PC/XT motherboard originally had a maximum memory of 256kbytes, but later upgrades allowed for 640kbytes. The board in the given link appears to be a clone, as it uses a NEC V20 microprocessor instead of the Intel 8088. The type of memory chips on the board are not clear, but it is possible to have 3 x 64kbytes or 3 x 256kbytes, with 9 chips in each bank due to the use of parity and bits from other chips to make an 8 bit byte of memory. The actual memory configuration would depend on the specific motherboard.
  • #1
jammy2012
1
0
Hi,

with regards to the DRAM of the IBM PC/XT motherboard, how come the maximum memory of the motherboard is 256Kbits and on the link below, it shows that there are 27 DRAMS of 256Kbits each, which therefore makes a total of 6912 Kbits (27*256) ?

http://upload.wikimedia.org/wikipedia/de/1/11/PCXTMainboard01.jpg

IS the board equipped with more memory that it can handle ?

Thanks in advance.
 
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  • #2
You motherboard is probably not an IBM motherboard but a clone. IBM used the Intel 8088 microprocessor and the one on the board is the NEC V20.

The XT went through a few revisions. Originally 256kbytes was offered, and a later motherboard upgrade allowed 640kbytes.

I cannot make out the type of memory chip on the board, so you could have 3 x 64kbyes or 192kbytes on board, or 3 x 256kbytes on board = 768kybes with 640kbyes as main ram and 128kbytes as extended.

The reason you have 9 chips in each bank is one bit of the 9th chip is used for parity and a bit from each of the other 8 chips to make an 8 bit byte of memory.
The actual configuration would be motherboard dependant.

You wrote "maximum memory of the motherboard is 256Kbits " when you actually meant 256kbyes.
 

Related to IBM PC/XT DRAM memory calculation

1. How much DRAM memory can an IBM PC/XT support?

The IBM PC/XT can support a maximum of 640 kilobytes of DRAM memory. This was the standard memory configuration for the PC/XT when it was first released in 1983.

2. Can the DRAM memory of an IBM PC/XT be upgraded?

Yes, the DRAM memory of an IBM PC/XT can be upgraded. The original 640 kilobytes of memory can be expanded to a maximum of 2 megabytes by adding additional memory modules to the expansion slots.

3. How is the DRAM memory calculated on an IBM PC/XT?

The DRAM memory on an IBM PC/XT is calculated by adding the memory of each installed module. For example, if there are two 256 kilobyte modules installed, the total DRAM memory would be 512 kilobytes.

4. What is the difference between DRAM and SRAM memory?

DRAM (Dynamic Random Access Memory) is a type of memory that uses capacitors to store data and requires refreshing to maintain the data. SRAM (Static Random Access Memory) uses flip-flop circuits to store data and does not require refreshing. DRAM is cheaper and more compact, while SRAM is faster and more expensive.

5. Can the DRAM memory of an IBM PC/XT be used for virtual memory?

No, the DRAM memory of an IBM PC/XT cannot be used for virtual memory. Virtual memory is a feature that was not available on the original PC/XT, and it requires a more advanced type of memory, such as DRAM or flash memory.

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