This means how much physical memory is used by programs on PC, this value is affected by SAI and all other programs running on Windows now.

More description:
Usually operating system(*1) has function named virtual memory, in very simplified explanation, virtual memory function locate the memory on HDD that applications using, and physical memory is used as cache. By this function, applications can use larger memory than equipped memory on PC, but if application use too large memory than physical (really equipped) memory, operating system need to access HDD more frequently and application speed become slower. This memory access on HDD is called 'Memory swap' or 'Page swap' or simply called 'Swap'.

Simplified examples for relation between physical memory and memory use and memory load are
- Physical memory 256MB, memory use 128MB, memory load 50%, comfortable, almost no swapping.
- Physical memory 256MB, memory use 300MB, memory load 100%(*2), too slow, frequently swapping memories.
- Physical memory 256MB, memory use 756MB, memory load 100%(*2), almostly not move, and system looks to work only for swapping.
- Physical memory 256MB, memory use 500MB, memory load 70%, looks comfortable, but when exchange foreground applications much swapping will occur.

(*1 The operating system described here is for PC like systems, and not include for embedded system like phone.
(*2 This value is reported by Windows, and actual maximum value looks 99% and not 100%.

- xxxMB reserved ... assigned memory amount
- xxxMB used ... really used memory amount

Comparing it to the dinner hall:
available memory amount ... all seats count in dinner hall
xxxMB reserved ... reserved seats count (this include where actually eating)
xxxMB used ... actually eating seats count

Standard hall seats count for 32bit Windows is 2048MB(2GB).

Note:
Enough memory for indicated maximum image size in [Option] > [Workspace Usage] is always reserved by SAI, but these memory not include for layers, please notice if you select larger image size in workspace usage, available memory for layers will be decreased.

32bit Windows usually allow to use only 2GB memory per an application, but if operating system's option is changed, Windows allow to use applications over 2GB memory (supported applications above 2GB only, and SAI is supporting). If you want to know how to configure this options, you can find more information linked below, but if you cannot understand meanings of below description, or uncertain about these risks, please never execute these settings. This is not standard support for this software and you need to execute at your own responsibility, although you inquire any more questions about this matter, we don't answer any more.

Reference:
Available switch options for the Windows XP and the Windows Server 2003 Boot.ini files

SAI's primary aim is more speed and quality, so currently we don't use any type of memory compression like technology, because these technology has bad effect for speed. but we think there are less problems except for too large image or too much layers that not match for actually equipped memory on PC.

We select 64bit per pixels for both speed and quality. In the first stage of development, we carefully tested both 32bpp and 64bpp, and the result of 64bpp was better than 32bpp both speed and quality. Certainly more memory required than 32bpp, but for our primary aim, 64bpp is more worthy we thought.

If you select very huge 'Maximum Canvas Size' (like 8000 x 8000 pixels) in SAI options, this sometimes cause memory shortage of each layer memory. In this case selecting minimum 'Maximum Canvas Size' for current drawing picture's size can be more efficient memory usage.

Considerable reasons are:
Memory shortage
If too large picture to allocate enough memory is read, the error message 'Opening canvas failed' will be shown. We are considering to provide more information for this error message in next release of SAI.

SAI file is broken
If broken SAI file is read, the error message 'Opening canvas failed' will be shown, this is almostly cause machine trouble of HDD etc. We are considering to provide more information for this error message in next release of SAI.

PNG file errors
In Ver.1.1.0, if the PNG reading is failed this cause access violation error(EXCEPTION_ACCESS_VIOLATION), this problem occur when the file viewer creating thumbnails. We recognize this is bug so we will fix it in next release of SAI. In current version's solution to avoid these problem is separate these (reading failed) PNG files from the file viewer's displaying folder.

JPEG file error
In Ver.1.1.0, if the Exif resolution embedded in JPEG file is 0/0 this cause division by zero error(EXCEPTION_INT_DIVIDE_BY_ZERO), this problem occur when the file viewer creating thumbnails. We recognize this is bug so we will fix it in next release of SAI. In current version's solution to avoid these problem is separate these (reading failed) JPEG files from the file viewer's displaying folder.

The .sai format is designed to detect data breakdown strictly, but some of other formats don't care the little broken data, so in this case not only .sai format but also other files may be broken.

If some of .sai files couldn't be opened without relation in their file size, please check the storage drive or their information may be broken. It is thought that caused by suddenly power supply OFF and failed to complete writing entire file information, or caused by longevities or breakdown of each devices. If you use USB storage, it may be caused by removal without 'Safely Remove Hardware' operations from taskbar.

Followings are notifications of some kind of drives:

- HDD(Hard Disk Drive)
These kind of drives are weak to heat. If used not enough cooling environment or temperature is largely changing situations, this cause shorten the longevities of them.

- Flash SSD(Solid State Drive) or USB Flash Memory
In these kind of drives the cells become deteriorated gradually on each data writings. Deterioration of cells cause data writing failure and files become disappear or broken. If without any data writings but it is said that each cells only keep data about ten years. Of course each products of this kind is improved day and day, but you should know they has longevity on readings and writings.

It seems that the file viewer is displayed outside of your monitor, in this case first close the file viewer with Esc key, and select 'Reset All Window Positions' with right-click menu from titlebar or taskbar icon.

This occurs by some programs that inject to other programs to modify the actions or extend system operations, some of these programs change the FPU (Floating-Point-Unit) precision and rounding settings when they inject to other programs. In this case SAI application cannot calculate expected result not only zooming but also any other internal calculations, so we cannot assure the software workings correctly in these environment. This is wrong way of injection programings, but we reported the DLLs that build by C++Builder or Delphi with VCL option change them. These DLLs using VCL is expected to use in the programs that is compiled by C++Builder or Delphi, so using these DLLs for general injection is programmer's mistake, please don't use these kind of software.

And we reported that the PC is infected by computer virus like 'Conficker' or 'Downadup' 'Downada' 'Kido' etc. These virus infect via USB thumb drive. Please check the computer virus and if infection is found please remove them.

Considerable reasons are:

Stroke stabilizer settings become S-1 to S-7.
If the stroke stabilizer settings on quickbar or each tools become S-1 to S-7, please set stroke stabilizer as non S-x settings.

Other application occupying CPU usage is running.
Please run the Windows task manager(*1) and check 'CPU Usage' on 'Performance' tab, although you don't touch your PC but CPU usage become not near 0%, this means some programs waste to use CPU, when using SAI please turn off these programs. For example recently some user report us the Google toolbar use much CPU usage.

(*1) The Windows task manager can start from right clicking menu on task bar.

Digitizer driver made by Wacom malfunctions
Please refer the below topics.
Q. Previously I could draw fine strokes, but suddenly I cannot draw them.

SAI only work on Windows, and we have no development plan for Macintosh port.