Those are all 4MB SIMMs.

Determining capacity from the numbers on chips is pretty simple. When you look at something like "4m x 1" it actually means 4 megabits, by 1 bit wide... it's easier to think of it in terms of columns, you have 1 column with a capacity of 4 megabits. There are 8 bits in a byte, so you divide the 4 megabits (4096 kilobits) by 8, to get 512 kilobytes. You have 8 of those 512KB chips on the SIMM, which add up to give you a total of 4MB.

Another common chip, often found on old video cards, is the 256k x 4. That means 4 columns of 256 kilobits each, giving you a total of 1 megabit (1024 kilobits). Divide that by 8 to convert it to bytes, for 128 kilobytes per chip.

You'll probably notice that on 8 bit chips, it works out more directly. The math is the same, it's just that the steps happen to cancel out. For example, a 32mb x 8 chip is 32 megabytes... it's 32 times 8, divided back by 8.

Oh, i thought it was something like that, now i understand fully, thanks!
Also, the fastest 30 PIN SIMMs were 50ns, right?

I'd imagine so. I've actually never seen any 30 pin SIMMs faster than 60ns, and even those are fairly uncommon... the 50ns ones must be pretty rare.

Oh, interesting.
I bought these for around 3$. What is the known maximum of these SIMMs? ( 16MB? )

Yep, 16MB is as high as they go. And that's not an arbitrary number... they use 24-bit addressing, which can't recognize anything more than 16MB per SIMM.

Cool. Thanks a lot for your replies, now i know more about them 😀

Old Thrashbarg wrote:

I'd imagine so. I've actually never seen any 30 pin SIMMs faster than 60ns, and even those are fairly uncommon... the 50ns ones must be pretty rare.

I barely even found any 50ns 72p SIMMs. All I once saw was a pair of 8MB 72p SIMMs that were 50ns. The rest were always 60ns or slower.
Never even knew 50ns 30p SIMMs existed!

Heh 😁
Want me to take a picture of them?

Stojke wrote:

Heh 😁
Want me to take a picture of them?

Please do! 😁

Sure thing! I will update the first post as soon as i get batteries for my photo camera 😀
I have contacted the guy that sold them to me over a message to see if he has any more.

did you buy all four pcs for just 3 dollar thats really cheap?

Yes, all 4 for 3$.

Damn... it's hard to find a quad of 4MB SIMMs of any speed for that kinda price. That's one hell of a lucky deal you got there.

Totally true, even around these parts (180 miles to the north of Serbia) the 60ns SIMMS go for about 4 USD A PIECE - that is 16 for a "kit". All sellers who know the goods ask this price at least.
Chances are better with people who do not even WANT to know the content of "bundles" they are selling - but then you need razor-sharp pictures or each item, which they usually do not provide. Then you ask them to post good pics or spell out the serials - potential buyers will swam in an instant and push the bids sky-high 😢
(I only have 3 16MB kits, so I am using 1 kit in my Amd 386 and keep the rest as spare.)