PC memory may use the following access methods:
was used in all PCs until the late 1990s, uses a window of fixed
minimum duration to determine when operations may occur. If the CPU
has transferred data while a window is open, and if a subsequent
clock cycle occurs while that window remains open, the CPU cannot
transfer additional data until the next window opens, thereby wasting
that clock cycle. Asynchronous operation forces the CPU to conform to
a fixed schedule for transferring data, rather than doing so whenever
All forms of asynchronous DRAM are now obsolete. Although asynchronous DRAM is still available, it costs so much per megabyte that it seldom makes sense to buy it. For example, in late 2001, SDRAM DIMMs sold for about $0.15 per megabyte while asynchronous DRAM SIMMs sold for between $1.50 and $12.00 per megabyte, depending on capacity and type. Asynchronous DRAM is available in the following types:
FPM was commonly used on 486 and earlier systems, and may be installed in early Pentium systems. FPM is not supported by recent chipsets. Although you can migrate FPM DRAM from an old Socket 5 or Socket 7 system to a newer Socket 7 system, it is good for little else. You may be able to install surplus FPM DRAM in your laser printer.
EDO, also sometimes called
Hyper Page Mode DRAM, is marginally faster than FPM, is still available in all common ...