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Zero-based deep space photography 10.5: Memory, bit, and Byte
2020 / 06 / 15


       Recently, a kid told me that he bought a 256MB device, but the store claimed that the memory was 2Gb, and that there was no difference between the two.The kid was wondering why 256MB was equal to 2Gb.What's the difference between GB and GB?How many gigabytes of memory do we mean by GB or GB?So Today Lee is going to talk to you about two basic concepts in computer science: a bit and a Byte.Although this content is far from deep space photography, but in the final analysis, the astronomical camera is also a digital device, there will be such a thing as memory, so I will take this opportunity to give you a common sense.



      Bit and Byte are two different levels of concepts.Bit (Chinese literal translation bit), commonly known as little B, is the bit in binary digits, the unit of measurement of information, and the smallest unit of information. It is also the basis of computer operation.A Byte, commonly known as a large B, is the basic unit of account for the size of a computer file. A Byte consists of eight bits, or 1Byte=8 bits.So let's go back to the above question: is it true that the merchants met by the children said 256MB=2Gb?That's right.256*8=2048, so 256MB=2Gb fine.But isn't that still weird?

     Yes, conversion itself is not a problem, the problem is that we usually talk about memory in terms of big B instead of small B.For example,QHY new-generation cameras, such as QHY268 and QHY600, are all 1GB/2GB, which are all good Big B.
     As mentioned above, Byte is the basic unit for measuring the size of a computer file, so when we talk about memory, storage, etc., the default unit is bytes, not bits.For example, Zhang SAN buys a 32GB USB flash drive, which is 32GB. If Zhang SAN forcibly says that he bought a 256Gb USB flash drive, it is not bad, but it sounds strange, and Zhang SAN knows exactly how many things can be packed.As for little B, its usual application is in transmission, such as broadband.

    For example, when you're measuring the speed of a network, you might be impressed with the MBP /s unit.Of course, its 8-bit conversion ratio still exists. 
     For example, Zhang SAN heard a salesman from a brand saying that its broadband download speed was as high as 256MBP /s and he thought that 200 megabytes was absolutely enough to install it. However, in fact, when converted into our common byte units, his theoretical maximum download speed could only reach 256/8=32MB/s.But it's still a lot faster than the Internet in my college dorm.

    This is actually a little convoluted for some zero-based computer users, so even when talking about transmission speed, bytes (big B) are being used more and more to make it easier for more people to understand.Although in most cases no one or business will cheat in this area, if you do encounter people in this area, you need to identify yourself. 


      So let's go back to business as usual.What does large memory mean for an astronomical camera?Now CMOS is making rapid progress. The latest 16BIT chip is very memory consuming, and the previous small memory has been difficult to meet the high requirements of astronomical photography for the shooting volume.

      For example, for QHY600, the capacity of a 16-bit dark image is up to 120MB, and the output frame rate of the camera at full resolution is up to 2.5FPS, which means that the data volume of one second has reached more than 300MB.If the memory is only 256MB, it will burst in seconds.With 1GB of ram, you can have a buffer of about 3 seconds, which means that even in some extreme cases, there is a delay of a second or two due to some kind of BUSY CPU (such as processing network connection, etc., or image processing and parsing of large amounts of data).

     Then 1GB of memory is also guaranteed not to lose frames.This is also why the QHYCCD USES 1GB of memory under the QHY600 photography edition and 2GB of memory under the QHY600 Pro edition.And smoother transfers require more than just memory.In addition to using 1GB and 2GB of memory, the new line of cameras has a 32-bit data line width instead of a 16-bit data line width.The 32-bit wide memory can transfer 4 bytes at a time. Compared with the 16-bit wide memory, which can transfer 2 bytes at a time, the data throughput is doubled, thus significantly improving the camera's transmission performance in large capacity and high frame rate, avoiding the occurrence of data bottleneck and thus avoiding the occurrence of lag.

     Of course, in some scientific applications, memory may also be used for some auxiliary calculation, and other auxiliary processing.In this case, a little more memory always pays off.While 4GB is still widely available on many desktops, the new QHY camera alone has 1GB/2GB.When the new generation of cameras have a new generation of new design, QHYCCD will never stand still, but hope to continue to give users advanced products.Although the cost of such memory is high.But delivering the value that users deserve is the principle of QHYCCD.


      Science is an unpretentious thing, but if more people understand why, it will not be boring.Our deep space science series recently received attention and support for more and more fans, there are also some do not know to have sprouted new watch circles accompanied by top level bosses give us the content of the details provided valuable advice, we have made correction, objective, accurate and easy to popular science, let astronomical photography is no longer a black box.Chip theory is coming to an end, the actual combat has been arranged, please look forward to oh ~


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