10/23/2023 0 Comments Data punch tape creatorEach column consisted of 12 places, so you might call it 12 bits, but the encoding didn't use all possible combinations. That "3000 punched cards" statement was what I'd call "advertising language", mixing in a lot of usage assumptions, and effectively comparing apples with pears.Ī standard punched card could hold 80 columns of data, with each column typically representing 1 possible character of a text line. In more understandable terms, that would be about 100 bytes, give or take a few bytes. The total information-theoretic practical capacity of a card will be, depending on the quality of the card stock, about 768-848 bit maybe a little less if we have to adjust the encoding to prevent long sequences of consecutive punches in one row. Therefore, each column can carry the amount of information equal to log2(1586) = 10.6 bit (or, for up to 4 punches, log2(794) = 9.6 bit). The number of 12-bit codes with up to 5 bits set is 1586 out of 4096 (for comparison, the number of 12-bit codes with up to 4 bits set is 794). Let's be generous and say that a card maintains enough rigidity with up to 5 holes per column (encodings existed allowing up to 6 holes for some characters, for example, the double quote in modified EBCDIC, which was represented by punches in rows BA8421, but they were rare). To find out the information capacity of a punched card, we need to consider the main limitation: the overall percentage of holes on a card must be substantially less than 50% for it to maintain rigidity and not to jam. This makes the idea of a punch card only averaging 26 bytes or 26 characters far more believable and thus IBM's estimate of 3000 punch cards equal to 80KB of magnetic binary storage is a boastful but not entirely inaccurate number. If your punch cards stored employee data then each card would be just one employee or if they stored programming code then each card would store a single line of code. So instead punch cards tended to have empty space on them. Imagine if every time you wanted to insert a character you had to repunch the the entire deck of cards (or at least those past the insertion point) in order to shift them all by one. Rather for purposes of practicality each card was treated like a seperate record. However a stack of punch cards was not normally treated as a single continuous stream of data. While there were several different character sets depending on the machine or programming language you were normally limited to 64 symbols (6 bits) per column, meaning a maximum of 60 bytes per punch card.Īt 60 bytes per card we'd still need less than 1400 to store 80k. IBM punch cards were designed around only having 1-3 holes per column representing numbers, letters and symbols. One is that you generally didn't treat the holes on a punch card as binary, doing that would weaken it too much and it would fall apart in the machine. Nope, beside the fact that a punch card does not hold bytes but characters, it's 80 per card.ģ000 might be a slight exaggeration (standard IBM punch card had 80 columns with 12 rows) but there are some factors that make it so that you can't just treat a punch card as 80 or 120 bytes. so the max storage capacity of 1 punched card would be roughly 26bytes 296 KiB (74 tracks with 8 sectors, each 512 bytes)Ģ37 KiB / 3000 gives about 80, the size of a punch card.īottom Line, both numbers are right in being about firsts, but not related.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |