Most are packet-switched, like Telenet, Tymnet, and other major players. The ill-fated Datran and a couple of others are circuit switched like a telephone system. Anyone can walk up and use this terminal, connected to a timeshared mainframe computer, for posting messages and announcements. That's a radical idea when computers are mostly inaccessible to ordinary people, and seen by the counterculture as tools of government and corporate power.
It was an attempt to lower maintenance costs while bolstering disk drive reliability. It was initially released with a 5 MB capacity, and two years later a 10 MB version was put on the market.
Ziv arrived in Cambridge, Mass. His Ph. So if you invest the computational effort, you can know you are approaching the best outcome possible. Ziv contrasts that certainty with the uncertainty of a deep-learning algorithm. It may be clear that the algorithm is working, but nobody really knows whether it is the best result possible.
He found this work less beautiful. That is why I didn't go into real computer science. Then in , with several other coworkers, he joined the faculty of Technion. Jacob Ziv with glasses , who became chair of Technion's electrical engineering department in the s, worked earlier on information theory with Moshe Zakai.
The two collaborated on a paper describing what became known as the Ziv-Zakai bound. The state of the art in lossless data compression at the time was Huffman coding.
This approach starts by finding sequences of bits in a data file and then sorting them by the frequency with which they appear. Then the encoder builds a dictionary in which the most common sequences are represented by the smallest number of bits.
This is the same idea behind Morse code: The most frequent letter in the English language, e, is represented by a single dot, while rarer letters have more complex combinations of dots and dashes. It requires two passes through a data file: one to calculate the statistical features of the file, and the second to encode the data. And storing the dictionary along with the encoded data adds to the size of the compressed file. Ziv and Lempel wondered if they could develop a lossless data-compression algorithm that would work on any kind of data, did not require preprocessing, and would achieve the best compression for that data, a target defined by something known as the Shannon entropy.
It was unclear if their goal was even possible. They decided to find out. The two came up with the idea of having the algorithm look for unique sequences of bits at the same time that it's compressing the data, using pointers to refer to previously seen sequences. This approach requires only one pass through the file, so it's faster than Huffman coding.
Let's say that first incoming bit is a 1. Now, since you have only one bit, you have never seen it in the past, so you have no choice but to transmit it as is. So you enter into your dictionary Say the next bit is a 0. So in your dictionary you now have and also Here's where the pointer comes in. The next time that the stream of bits includes a or a , the software doesn't transmit those bits.
Instead it sends a pointer to the location where that sequence first appeared, along with the length of the matched sequence. The number of bits that you need for that pointer is very small.
If the program appeared more than once, they didn't republish the synopsis. They just said, go back to page x. Decoding in this way is even simpler, because the decoder doesn't have to identify unique sequences.
Instead it finds the locations of the sequences by following the pointers and then replaces each pointer with a copy of the relevant sequence. The algorithm did everything Ziv and Lempel had set out to do—it proved that universally optimum lossless compression without preprocessing was possible. Eventually, though, researchers recognized the algorithm's practical implications, Weissman says.
Ziv and Lempel kept working on the technology, trying to get closer to entropy for small data files. That work led to LZ In January , a photograph of the Altair appeared on the cover of the magazine Popular Electronics.
Roberts had hoped to break even by selling Altairs. Within three months he had a backlog of 4, orders. The kit offered by MITS represented the minimum configuration of circuits that one could legitimately call a computer.
It had little internal and no external memory, no printer, and no keyboard or other input device. Most purchasers found the kit was difficult to assemble, unless they had experience with digital electronics and a workbench fitted out with sophisticated test equipment.
And even if one assembled the kit correctly it was sometimes difficult to get the Altair to operate reliably. Gift of Forrest M. Nominate this object for photography. We got one of the original Altair in my department at North Carolina school of the Arts in It was a marvel that opened the world of digital computers to many of the students who like myself went on to successful careers as computer engineers.
It opened my eyes to the possible. Rob Aronson Mon, The Altair in your collection was one of the first five assembled units. Ed Roberts gave me this Altair in return for my writing the first operator's manual. While some builders of the kit version had problems, "sophisticated test equipment" was not necessarily required.
MITS did not have enough time to build a second prototype, so Yates simply filled a box with switches, LEDs, and rudimentary circuitry to make the lights flash. Shortly before press time, the computer still did not have a name.
Les Solomon liked to spin this yarn about his daughter naming it:. After dinner one night I asked my twelve year-old daughter, who was watching Star Trek, what the computer on the Enterprise was called.
But Forrest Mims tells a less interesting although maybe more factual story: Solomon and other editors were discussing the name. Altair is the 12th brightest star in the night sky. Despite the excitement at MITS and Popular Electronics, Roberts, even at his most optimistic, thought they could sell units they needed to sell units to break even. MITS was surprised to receive over 1, orders by the end of February, and over 2, by the end of May.
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